1. Field of the Invention
The present invention relates to a laser beam applying apparatus for applying a laser beam to a workpiece such as a semiconductor wafer and an optical device wafer.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines called streets are formed on the front side of a substantially disk-shaped silicon substrate to thereby partition a plurality of regions where semiconductor devices such as ICs and LSIs are respectively formed, thus forming a semiconductor wafer. The semiconductor wafer is cut along the streets to thereby divide the regions where the semiconductor devices are formed from each other, thus obtaining individual semiconductor chips. Further, an optical device wafer is provided by forming photodetectors such as photodiodes or light emitting devices such as laser diodes on the front side of a sapphire substrate. The optical device wafer is also cut along the streets to obtain individual optical devices divided from each other, such as photodiodes and laser diodes, which are widely used in electric equipment.
As a method of dividing a wafer such as a semiconductor wafer and an optical device wafer along the streets, there has been proposed a method including the steps of applying a pulsed laser beam having an absorption wavelength to the wafer along the streets to thereby form laser processed grooves on the wafer along the streets and next breaking the wafer along the laser processed grooves. Further, there has been proposed a laser processing apparatus in which the spot shape of the laser beam is formed into an elliptical shape to improve a processing accuracy. This laser processing apparatus includes spot shaping means provided by a cylindrical lens to form the spot shape of the laser beam into an elliptical shape (see Japanese Patent Laid-open No. 2006-289388, for example). As a method of forming the spot shape of the laser beam into a predetermined shape with a relatively simple configuration, the use of a diffractive optic element (DOE) is also known.